1. Field of the Invention
The present invention relates to an X-ray object positioning apparatus for use in an X-ray imaging apparatus which radiates X-rays on an object and produces an image of an X-ray absorption coefficient of a desired region of the object by X-rays transmitted through the object and an X-ray imaging apparatus provided with the same.
2. Prior Art
Some X-ray imaging apparatus for executing panoramic radiography of a dental jaw bone in dental field need accurate radiation of X-rays on a desired region of an object. For this purpose, X-ray positioning means for use in an X-ray imaging apparatus for positioning the object at a desired imaging position is used.
One example is an X-ray object positioning means for use in an X-ray imaging apparatus which uses guide beams in X, Y, and Z directions showing X-ray imaging position and sets relative positional relation between the object and an X-ray generator in such a manner that these guide beams are radiated at desired positions of the object.
However, in such a method, it has been advantageous to rough positioning of the whole object or its parts. If X-rays are radiated only on a local region in the object and an X-ray image of that region is required, for example, an image of a few teeth around a carious tooth is required, positioning should be executed depending on guide beams radiated on the outside of the object, which is a human head, and assuming the radiated region inside thereof, thereby enabling accurate positioning.
Furthermore, anatomical knowledge on the radiated region of the object is required for accurate positioning. There has been a problem that only a skilled operator can execute radiography and there has been a high possibility of mistakes.
The present invention has been proposed in view of the above-mentioned problems. It is an object of the present invention to provide an X-ray object positioning apparatus for use in an X-ray imaging apparatus which can execute positioning accurately without depending on experience and hunch when the radiation region of X-rays, namely an X-ray imaging target area, is in the object body, and to provide an X-ray imaging apparatus provided with this means.
According to the X-ray object positioning apparatus for use in an X-ray imaging apparatus of the first embodiment of the present invention, when an object model is fixedly held by object fixing means and either one of the object fixing means or an X-ray generator for irradiating X-rays toward an X-ray imaging target area, or both of them are moved by imaging position moving means so as to conform the X-ray imaging target area with a predetermined position of the object, position of an imaging target area index is set on an object model, without irradiating guide beams on the surface of the object like prior arts. Positioning is executed in such a manner that a model imaging reference point of the object model and an actual imaging reference point of the object are conformed, then the object model and the imaging target area index are displayed on display means, and position of the imaging target area index is set on the object model while watching that the relative movement of the object is shown as the movement of the imaging target area index against the object model.
Here, the X-ray imaging target area means a target area of X-radiation and has different meanings depending on X-ray imaging methods. It is for example a part of the object on which X-ray radiation beams pass through in case of one-shot imaging. It is a part of the object on which X-ray radiation beams pass through from start to end of scanning in case of scan radiography. Further, in case of panoramic radiography, it is a predetermined area around the movement trace of the rotation center of the rotary arm. As for an ortho X-ray CT radiography, it will be described later. The imaging target area index is the one shown on the display means by employing the X-ray imaging target area as a model.
The object model is that the object using as a model is diagrammatically represented on a plane view and, for example, includes a view wherein the object is comprehended on an one-dimensional coordinate of only a Z-axis, not only the view wherein the object is comprehended on a two-dimensional coordinate of an X-axis and a Y-axis.
Accordingly, comparing with presuming from outside, the position of the X-ray imaging target area in the object can be clearly understood and can be set on an objected local region easily and no mistake without requiring anatomical knowledge and experience on the object.
According to an X-ray object positioning apparatus for use in an X-ray imaging apparatus of the second embodiment of the present invention, in case that an object and an X-ray imaging target area are relatively moved, an object model is moved while an imaging target area index is fixed on the display. Therefore, the movement of the object against the fixed X-ray imaging target area can be comprehended by intuition so that positioning of the object can be easily done with no mistake.
Further according to an X-ray object positioning apparatus for use in an X-ray imaging apparatus of the third embodiment of the present invention, in case that an object and an X-ray imaging target area are relatively moved, an imaging target area index is moved while an object model is fixed on the display. Therefore, when the X-ray imaging target area is smaller than the object, such a display is possible that the imaging target area index is moved within the display area of the object model while the object model is shown on the display, thereby enabling effective usage of the display screen. Moreover, it is easily understood where the imaging target area index is on the object model, namely where it is on the whole object.
In an X-ray object positioning apparatus for use in an X-ray imaging apparatus of the fourth embodiment of the present invention, the relative moving relation between an object model and an imaging target area index on the display is varied in accordance with the relative moving relation between an actual object fixed on an object fixing means and the X-ray imaging target area.
In other words, in case that the object is fixed and the X-ray imaging target area is moved, the object model is fixed and the imaging target area index is moved on the display. On the other hand when the X-ray imaging target area is fixed and the object is moved, the imaging target area index is fixed and the object model is moved also on the display.
Therefore, actual movement of the object conforms to its movement on the display so that movement of the object can be understood by intuition and the object can be easily positioned with no mistake.
In an X-ray object positioning apparatus for use in an X-ray imaging apparatus of the fifth embodiment of the present invention, before positioning an X-ray imaging target area by relatively moving an object and an X-ray imaging target area, an actual imaging standard point of the object and a model imaging standard point of an object model are accorded by means of calibration means. Such defined process is a natural pre-process for accurate positioning and as a result the standard point of the actual object and that of the object model are conformed. Accordingly the movement on the display accords with the actual movement, thereby enabling accurate positioning.
An X-ray object positioning apparatus for use in an X-ray imaging apparatus of the sixth embodiment of the present invention combines guide beams which have been used as positioning means from outside of the object in prior arts. Such guide beams are used as calibration means for according a model imaging standard point of an object model and an actual imaging standard point of the object.
That is, a standard point is selected at a position which is relatively near the object surface, at a root apex of front teeth in case of a dental jaw. Because the rood apex of front teeth corresponds to a side part of front lips seen from outside of the object which is a human head, both standards are considered to be agreed when guide beams conform to the side part of front lips of the object.
In such a manner, calibration can be executed without touching the object and further guide beams can be a rough standard representing the X-ray imaging target area on the object surface, thereby achieving easy comprehension of the target area.
Calibration means isn""t limited to such guide beams. A method using a terminal which touches a standard point of front teeth may be employed or a method using a dental articulation model of the object may be executed for purposes of accuracy in dentistry.
An X-ray object positioning apparatus for use in an X-ray imaging apparatus of the seventh embodiment of the present invention is characterized of a relative display way of an object model and an imaging target area index on display means. If the object size is varied, its object model size isn""t changed accordingly, but the size of the imaging target area index is changed without changing the displayed size of the object model. Therefore, the image of the area size covered by an X-ray imaging target area against the object size can be easily comprehended, thereby enabling easy judgment of radiation extent.
The display area of the display means is generally limited. However, in such a case mentioned above, the object model size showing the entire area where the imaging target area index is moved can be constant so that the display area of the display means can be effectively used.
An X-ray object positioning apparatus for use in an X-ray imaging apparatus of the eighth embodiment of the present invention is characterized of a relative display way of an object model and an imaging target area index on display means like the seventh embodiment. In this embodiment, the imaging target area index is constant and the object model size is changed unlike the embodiment 7 wherein the imaging target area index is varied in inverse proportion to the object size. Accordingly, such an embodiment is suitable for an actual imaging and the image of the area size covered by an X-ray imaging target area against the object size can be easily comprehended, thereby enabling easy judgment of the extent of radiation. Moreover, the size relation between the object and the object model can be sensuously understood.
According to an X-ray object positioning apparatus for use in an X-ray imaging apparatus of the ninth embodiment of the present invention, a coordinate axis index which defines a central position of an imaging target area index is shown on display means. The central position, the rotation center of a rotary arm for X-ray radiation in case of a panoramic radiography, can be comprehended at ease, thereby achieving usability.
An X-ray object positioning apparatus for use in an X-ray imaging apparatus of the tenth embodiment of the present invention comprises coordinate axis rotation means for rotating a coordinate axis for X-ray object positioning against an imaging standard coordinate system. The coordinate axis after rotation can be a slice standard axis for hewing out sliced sectional images of the obtained three-dimensional X-ray image. In this case because an object model is shown on display means in such a shape along the imaging standard coordinate system, the slice standard axis angle at an imaging position, namely a slice angle, can be set so as to along with the teeth arrangement of a dental arch if the object is a dental arch. Therefore, slice angle setting isn""t required to be done again in case of hewn-out display.
Here, the imaging standard coordinate system indicates a coordinate system which becomes an imaging standard of the X-ray imaging apparatus adapted with the X-ray object positioning apparatus. If the object is a human head for example, a median line of the human body becomes a standard, its vertical direction is a Z-axis, its lateral direction for the object is an X-axis, and its back and forth direction for the object is a Y-axis. Its original point can be an occlusal surface of the dental arch of the objects head on the median line.
According to an X-ray object positioning apparatus for use in an X-ray imaging apparatus of the eleventh embodiment of the present invention, in case that an object to be radiated is a dental jaw bone as one of special examples, its vertical positional arrangement is possible up to a maxillary antrum. Such an apparatus meets the requirements of actual diagnosis.
In an X-ray object positioning apparatus for use in an X-ray imaging apparatus of the twelfth embodiment of the present invention, the X-ray imaging apparatus provided with the X-ray object positioning apparatus is limited to an ortho X-ray computed tomography apparatus.
The ortho X-ray CT apparatus has been proposed by the applicant of the present invention and its details are described in JP-A-2000-139902. According to the apparatus, conical X-ray beams are locally radiated only on a local region of an object while rotating a rotary arm suspending an X-ray generator and a two-dimensional image sensor opposed each other. Its imaging condition is such that conical X-ray beams covering only the local region to be pictured are radiated from the X-ray generator and the rotary arm is driven to be rotated while fixing a rotation center on the center of the local region to be pictured.
The electrical signals on the two-dimensional X-ray imaging sensor obtained by thus radiating are digitalized and backprojected so as to obtain a three-dimensional X-ray absorption coefficient of the irradiated local region, thereby obtaining optional sectional images of the local region. Further according to this, the exposed dose of X-rays can be reduced to a few tenths or a few hundredths compared to the prior art which radiates X-rays on the entire object.
This imaging method is based on an idea that the projection data of the local region on which conical X-ray beams are locally radiated is always obtained, but the conical X-ray beams temporally transmit the other area surrounding the local region according to rotation compared to the local region and there is only a minute affection on the projected data, so that the affection on the projection data other than the local region can be almost ignored in case of backprojection.
The X-ray object positioning apparatus of the present invention is suitable for positioning in case of local radiation which is considered to be most important for such an ortho X-ray CT apparatus.
Further according to the X-ray object positioning apparatus of the present invention, the object is limited to a dental jaw bone and the X-ray imaging target area is limited to the area which is always locally radiated. In such a case requirements for X-ray imaging target area positioning is largest and the effects of the present invention can be highly brought out.
An X-ray object positioning apparatus for use in an X-ray imaging apparatus of the thirteenth embodiment of the present invention is the twelfth embodiment having the characteristics of the eleventh embodiment so that both effects of the embodiments can be multiply achieved.
An X-ray imaging apparatus of the fourteenth embodiment of the present invention is provided with an X-ray object positioning apparatus having the characteristics of the first to the thirteenth embodiments so that each effect of the positioning apparatuses can be exerted as an imaging apparatus.
An X-ray imaging apparatus of the fifteenth embodiment corresponds to the X-ray imaging apparatus providing the X-ray object positioning apparatus having the characteristics of the fourteenth embodiment, namely the X-ray object positioning apparatus of the twelfth and the thirteenth embodiments. The X-ray imaging apparatus has the characteristics of these embodiments as an imaging apparatus.